Sunday, 29 June 2014

As I mentioned previously as part of my overview of the weasel family, we used to think that the "common", or Eurasian, badger inhabited much of that continent, with individuals found from Britain to Japan. We now know that that's not the case; there are at least three different species of badger within this area, albeit very closely related.

In Britain and Ireland, we think of badgers as living in communal setts, with multiple different family groups sharing the same network of tunnels and chambers, that may have built up over generations. Yet, while this is true in the British Isles, it isn't true anywhere else, even when we are looking at the exact same species where it lives on continental Europe. Here, as with most other members of the weasel family, European badgers live alone when they aren't raising their young.

The reason for this is thought to be a combination of Britain's climate and a diet rich in earthworms.The frequent rains in the British Isles are good for earthworms, and there are so many available to eat that the badger population in the islands is unusually high, something that they deal with by crowding together in larger groups. Elsewhere in Europe, there are less earthworms, and the badgers have a broader diet, but one that requires them to defend their territory from others of their own species if they don't want to starve.

Sunday, 22 June 2014

Once each year, animals like seals and sea lions haul themselves out of the water to spend time on rookeries located on remote coasts or distant islands. Once there, the females give birth to their young, raise them to the point that they can swim effectively, and then take part in the long orgy of reproduction during which the males fight for their affections. And then they all return to the water again, living out the rest of the year at sea.

For obvious reasons, nature documentaries tend to focus on this time of a seal's life. Scientists, too, know rather more about what the animals are up to when they're on land where they can see them, than they do about what they're up to when they're away from the coasts. Yet, fun though reproduction undoubtedly is, most of a seal's life is spent at sea, not at their annual breeding grounds. With modern tracking technology, however, we're beginning to get a better picture of what seals do during this time, and where they do it.

Take the northern fur seal (Callorhinus ursinus). Technically, these aren't seals, in the sense that they don't belong to the seal family, bur rather to the sea lion family. That's a bit confusing, so the term 'seal' is often used more broadly than that, and the two families are distinguished as 'earless seals' (the actual seal family, the Phocidae) and 'eared seals' (the sea lion family, including, of course, the sea lions themselves). That is, you can either consider sea lions to be a special kind of seal, or fur seals to be a special kind of sea lion. Or both, if you must. Take your pick.

Sunday, 15 June 2014

Over the last five months I have looked at the 22 widely recognised species of marmoset. However, as I mentioned back when I started, not all members of the marmoset family are actually marmosets. Almost all of the others are tamarins, the majority of which belong to the genus Saguinus, also known as the 'true' tamarins.

So what is the difference between a marmoset and a tamarin? On the face of it, they look quite similar, and, indeed, being members of the same family, that's not entirely inaccurate. They're roughly the same size, have the same luxuriant fur, often with extravagant tufts, and have the same basic body plan, with a long non-prehensile tail, clawed toes, and so on. The most significant difference though, and the one on which they were first separated back in the early 19th century, is in the shape of their teeth.

Unlike marmosets, tamarins have prominent canine teeth in their lower jaw. These are often called "tusks", although by a strict definition, tusks have to project outside the lips (as they do in wild boars or elephants), which these don't. In fact, they're actually no larger than those of marmosets, they just look that way because the incisor teeth that separate them at the front of the mouth are of a more normal size. In marmosets, the incisors are elongated and cylindrical, forming a straight line with the top of the canines, but in tamarins, the closer in size to what you'd expect in monkeys, making the canines stand out.

Saturday, 7 June 2014

The island continent of Australia has today what is probably the strangest mammalian fauna of any continent. Yet it is also the continent that has, perhaps, suffered the greatest number of mammalian extinctions over the last 50,000 years or so. Many of those are relatively recent, or at least after the end of the last Ice Age around 10,000 BC. But even compared with the Australia of, say, the 18th century, the wildlife of Ice Age Australia looked pretty odd.

In climactic terms, Australia didn't suffer too badly from the Ice Ages. It's too close to the equator to have had ice sheets get anywhere near it, although doubtless there was rather more snow on the mountains. (Although perhaps not too much - even today, Australia is the only continent to lack glaciers). Then, as today, much of the continent consisted of desert, and the bits that weren't were mostly arid grassland, albeit with denser woodlands around the eastern and northern coasts.

Sunday, 1 June 2014

Chipmunks are a kind of small squirrel, found mostly in western North America. Spending the winter in underground burrows, they are more related to ground squirrels, such as prairie dogs and marmots, than they are to tree squirrels, such as the ubiquitous eastern grey. They share a lot of features in common with other squirrels, and I doubt it's much of a surprise to anyone that this is, indeed, what they are.

One thing they have in common with other squirrels is their habit of hoarding food. In fact, their scientific name, Tamias, is Greek for something like "steward" or "treasurer", implying an animal that carefully looks after its food stores. As with other squirrels, since they don't truly hibernate, this habit helps them to survive through the winter, especially in the colder or drier climates in which many of them live.

There is something of an art to this, since chipmunks (and squirrels in general) are no great respecters of property rights. If they can find somebody else's cache of food, they'll be in there like a shot.

They don't even particularly care if the cache was left by a member of their own species or not. If the owner is the same species as yourself then, well, he's probably a rival, since chipmunks aren't especially sociable. If, on the other hand, he isn't, then that's even less of an issue, since they all eat broadly the same kind of seeds and small nuts. This, however, leads to a problem - sure, you may be able to pinch his food, but what's to stop him pinching yours?

The trick, then, is to try and find somewhere to hide your food that's easy for you to remember, but hard for anyone else to guess. A bit like the password on your bank account, then. Not all chipmunks, it turns out, are equally good at this. Let's take a look, for example, at the two most widespread American species.